crushed LR plenum substrate

[MikeS]

Hi all

been working through some details of a plenum system for my new tank. Mojo has suggested crushed LR as a substrate above the plenum...

A thought popped into my head today about this, and a possible negative to using this type of substrate above a plenum. Live rock "sheds" detritus. If the LR substrate above the plenum sheds detritus into itself, particularly at the lower depths where flow in the tank and routine cleaning wouldn't reach it, wouldn't this speed up buildup in the substrate, with the resulting clog issuses like poor diffusion, conversion from anoxic to anerobic at the plenum, ect...

Thoughts on this?

MikeS

 

[Haole]

Good point MikeS.
I’m still trying to figure out where detritus comes from. lol
I guess it would have to do with how finely crushed the LR would be and the matter of how deep it would be. Someone correct me if I’m wrong, but isn’t a portion of detritus the end result of microbial activity? And this is a stretch.... but maybe in the lower anoxic zones of the crushed LR, detritus isn’t produced because of the lack of oxygen dependant microbes. (shrug)

 

[Scooterman]

It is a long chain microorganisms eating one portion of the previously processed waste (food to them) and also you need to consider the life of these last a very short time so they reproduce and die off rather quickly, they all push detritus from deep within the rocks, crushed rocks will allow more surface area but less depth. Your build up Don needs to be removed or drawn deeper into the plenum. Now how is this accomplished, you have to go back to plenum design again, we discussed several designs some proven & some experimental like the toilet effect Mike made, that was cool.

 

[NaH2O]

MikeS - what kind of flow is the tank going to have? I don't think the substrate shedding detritus is going to be an issue because of the small size. You're talking an average of 5mm pieces? How deep? My thinking is any crud (scientific ) will be broken down, as usual, but maybe processed better because it is live rock? Great question.

 

[MikeS]

The tank will have lots of flow (looking at around 25-30x turnover) and quite a bit of it will be directed parallel and just above the substrate via an internal CL type system I'm thinking of. This should keep a fair amount of waste suspended, and be very conducive to diffusion through the substrate and into the plenum. My concern however is what happens below the surface of the substrate itself, where the flow is no longer a factor. The substrate will be graded between 3-6mm...with the majority of the particles being around 4mm or so. I plan on a 4-5 inch deep bed above the plenum.

My worry is that if the rock is constantly shedding detritus into the substrate, there is a good possibility it may build up faster than it can be processed, clogging or even possibly crashing the plenum. And even if it is being processed fast enough, then I'll still be building up nutrients in the substrate faster than I would be if I were using a material that didn't shed, like aragonite or CC...

MikeS

 

[MikeS]

Also...the plenum will have an "active" ability similar to the one we discussed in the active plenum thread here, but will not be as intricate nor likley as efficient at removal...it will be plumbed for some drawoff "just in case"....

MikeS

 

[NaH2O]

Mike - I think, like with a DSB, bioload and husbandry are going to play a role. Unless you are stocking this tank to the gills (no pun intended), I can't imagine the live rock shedding so much that the bacterias can't keep up (unless you keep dumping that phyto in there ). The bacterial population would grow to the level it needs to be inorder to process the wastes. Over time that population would build, as the tank load changes. Are you going to boil the substrate before adding it? Another thing about the grain size, you should be able to give it some good siphoning to suck out some of the detritus. I'm not sure if any of this is accurate...I'm working it out in my head.

 

[mojoreef]

Any rock, sand, sponge or anything that is porious that will house bacteria will shed detritus so it doesnt really matter. CC is??? smaller peices of coral that has been crushed? so they have the same properties as LR rubble the only difference is the size of the particle, same thing applies for sand.

your good buddy


Mike

 

[MikeS]

I'm not sure if any of this is accurate...I'm working it out in my head.

I think you are on target Nikki...I'm hoping as well that the shedding issue will only minimally impact accumulation in the substrate, however, anything I can do to keep nutrient buildup in the substrate to a minimum IMO will be a plus in both effectiveness and lifespan of the system...

Mojo...I agree with your point on any porous material used will likely act the same...would I perhaps be better off then using a more dense material, like coarse aragonite gravel? Or will the negatives of aragonite not be worth the trade off of less shedding?

Thanks for the input everybody...

MikeS

 

[mojoreef]

What is the difference between aragonite and LR rubble


Mike

 

[Haole]

I was merely throwing my thoughts out there in hopes to obtain better clarification for myself on the how’s and why’s of detritus production.
Nearly twenty years in the hobby and still learning and learning and learning..... lol

 

[Haole]

What is the difference between aragonite and LR rubble


Mike

Doesn’t aragonite slowly dissolve where as LR rubble doesn’t at any significant amount?

I know.... I’m probably setting myself up on a trick question.... Right?

 

[MikeS]

What is the difference between aragonite and LR rubble


Mike

I would assume that the individual grains of aragonite are much less porous than the LR, thus less capible of harboring the numbers of bacteria internally....a more dense material...less "shedding"....

MikeS

 

[MikeS]

Doesn’t aragonite slowly dissolve where as LR rubble doesn’t at any significant amount?

I know.... I’m probably setting myself up on a trick question.... Right?

You are correct, aragonite is more reactive, particularly in the lower depths of a substrate where pH tends to be the lowest...

MikeS

 

[mojoreef]

Ok here is my reasoning. Chemically they are both the same calcium carbonate and their dissolving rate is also the same. CC, sand and/or aragonite gravel are usually mined above ground, sifted for size and then sold as different mix grades.
Aragonite gravel= having been above ground all bacteria have died, which means any nutrients locked into the bacteria are now part of the gravel its self. Being above ground also means that it has be exposed to decades of nutrient run off from surrounding eco systems. Aragonite can also be formed by critters such as snails and other shell bearing critters, when they form aragonite they use heavy amounts of P when forming it. Their is only one aragonite mine in the world (bahamas I think?) so it does come from a terrestrial source.
=LR rubble, Comes from a water source and is not subjected to run off. Bacteria are present and thus the nutrients are still bound to an organic source. Pouriocity is much better and will allow for internal nitrification and the production of soluble byproducts to be moved down into the bed through diffusion from water flow above. With the size you are looking for I dought they will have any denitrifing capabilities. Because of the size of the rubble I highly dought you are going to have any build up of detritus to shed, their is always going to be a byproduct from either of these two substraights, with the rubble you get a little more nitrifing bacteria, which I believe will enhance what you are trying to do.

Mike

 

[NaH2O]

A few questions. First, should the crushed LR substrate be cooked or boiled, in order to get rid of any detritus or dead organisms? If so, crush the live rock before cooking, or cook first then crush?

Second...is there going to be a maintenance routine in order to keep this functioning properly? Because of the grain size, the bed isn't going to be dependant on critters, like a DSB, so bacteria is going to be most important, right? How often should the crushed LR substrate be siphoned to remove detritus and other waste matter?

 

[MikeS]

Thanks mojo...I got your point...thanks for the clarification

Nikki...yes, I'm going to boil about 95 percent of it, leaving 5% untouched to re-seed the crushed LR as it cures...I'l probably crush it first then boil it...that way I think I can make sure that it's nice and sterile proir to curing...also I think the crushed product will shed considerably more waste in the boiling process than the larger rocks..

Right...the main means of diffusion into the substrate and plenum will be diffusion...as for maintenance, I'll probably siphon it off every time I do a water change (about once a week-10 days). I'd like to keep detritus buildup to a minimum in this system..

MikeS

 

[mojoreef]

Mike I would boil it all. and then reseed with a LR or even just a bottle of bacteria. That way you garrantee yourself clean substraight and the bacteria only that you want. Remember you are going to be adding new live rock so you will be getting side bar critters from thier along with the balance you your bacteria pop. This way it will give you the oppertunity to control what goes in through husbandry. As per maintence, with the sucking out of the plenum are from time to time I would just do a stir more then I would look to syphoning, but again that would depend on the bioload.


Mike

 

[NaH2O]

MikeS - are you going to suck out the plenum occasionally?? I thought the original plan was not to do that. Guess I should look back, or maybe you changed your mind? Could be I wasn't paying attention .

 

[MikeS]

Nikki...I'm going to plumb it so I can draw off the plenum itself if necessary...sort of a "just in case" feature...

Mojo...by syponing, I meant just gently vaccuming the upper level of the substrate...

MikeS